The long term objectives of this research are to develop quantitative methods that will enhance the capabilities of medical ultrasound to diagnose focal and diffuse liver disease. Progress during the current grant period has led to in vivo measurements of backscatter and attenuation in normal livers and livers of patients with diffuse disease. In addition new ways to quantify spatial autocorrelation functions from RF echo data and backscatter and attenuation coefficients with a clinical scanner were introduced. The clinical imager backscatter and attenuation technique has been termed "VSA." In the proposed grant period, the VSA method will be investigated thoroughly, defining limitations of accuracy and requirements for reference phantoms when broad-bandwidth instruments are used for backscatter and attenuation estimations. Clinical utility of VSA in veterinary medicine will be studied by applying it to ultrasound scans of the liver, prostate and spleen in sites where correlations with histology will be available. In addition, investigations using both RF echo data and VSA will continue to define "ideal" B-mode imaging and acoustic scattering characteristics of liver masses obtained during partial hepatic resections. We will define how image contrast, gray scale texture and RF echo signal parameters vary with frequency to help optimize imaging in intraoperative and laparoscopic ultrasound. We also will study the extent that ultrasound echo features of these tumors, obtained in an ideal environment, are degraded during sound transmission through the patient body wall. Extensive use will be made of tissue mimicking phantoms to test methodology and to understand image and echo degradation.